1. Field of the Invention
The present invention relates to a printing apparatus which performs a printing operation through a thermal transfer technique and a thermal transfer printing method which is used in the printing apparatus.
2. Description of the Related Art
In recent years, in accordance with the supply of digital cameras, there is an increasing demand for a photographic print similar to high-quality silver halide photography. As printing technologies for satisfying the demand for this photographic print, for example, there exists a printing technology of a thermal transfer type such as a thermal sensitive type, a thermal melting type, or a sublimation type.
In the printing technology of the thermal transfer type, for example, in the sublimation type, thermal energy controlled by an image signal is applied to a thermal head, and a color material (dye ink) on a thermal transfer sheet is sublimated in response to the thermal energy. Then, the sublimated color material is transferred onto a printing target medium. In this manner, a printing operation is performed on the printing target medium. According to the printing technology, since the color material in use is a dye ink, the color material is very clear and has excellent transparency. In addition, since it is possible to adjust the ink amount by minutely controlling the applied heat amount, the obtained image has an excellent grayscale property and reproducibility of neutral color. That is, it is possible to form an image similar to the silver halide photography.
Generally, the printing target medium used in the printing operation in the thermal transfer type includes an air gap layer which has a heat insulation function and is provided as an intermediate layer in addition to a dye storing layer for storing the color material. The air gap layer holds a heat generated from the thermal head so as to highly efficiently obtain thermal energy necessary for the transfer operation of the color material. For this reason, as the air gap layer, for example, a film provided with air gaps formed by adding microscopic particles to a thermoplastic resin and two-axially stretching the result, or a layer coated with a result formed by mixing hollow particles with a binder resin is used.
In detail, there is a proposal in which a polyethylene terephthalate (hereinafter, referred to as “PET”) film having a specific weight is used as a film for the air gap layer (for example, refer to JP-A-2004-181888). In addition, there is a proposal in which a thermal transfer receiving sheet has a sheet-like support formed of a cushion layer containing hollow particles and a thermoplastic resin film layer which are stacked sequentially on at least one side of a core layer, and an image receiving layer formed on the thermoplastic resin film layer, and the thermoplastic resin film layer is stacked on the cushion layer with an adhesive layer therebetween (for example, refer to JP-A-2005-169945). Further, there is a proposal in which a thermal transfer image receiving sheet provided with an image receiving layer provided on a support formed by pulp paper mainly containing wood pulp and synthetic pulp and receiving a dye transferred from a thermal transfer medium at the time of heating by thermal melting or sublimation, an intermediate layer is provided between a support and the image receiving layer, and the intermediate layer mainly contains the spherical hollow particles and the rubber elastomer fine particles (for example, refer to JP-A-H08-80685). Furthermore, there is a proposal in which a thermal transfer receiving sheet has a partition wall made of a polymeric material and keeps at least one side surface of a sheet-like support successively overlaid with an intermediate layer containing a hollow particle having pores inside and an image receiving layer, and, as the hollow particles, the intermediate layer contains at least hollow particles in which the partition wall is formed by the polymeric material having a glass transition temperature of 130° C. or more (for example, refer to JP-A-2006-96024).